1. Field of the Invention
This invention relates to a load-bearing structure for a continuous rolling mill for seamless tube making from axially bored blanks fitted over respective mandrels.
More specifically, this invention relates to a load-bearing structure for a continuous rolling mill, operating on the so-called restrained mandrel technique, and of a type which comprises a plurality of pairs of working rolls and related chocks and aligned at an alternate angle to the rolling axis.
With continuous rolling mills of the above-specified type, as utilized heretofore, the working roll pairs and respective chocks are supported on corresponding stands attached, in turn, to a load-bearing structure (bed or base of the mill), which is anchored securely to the floor. Usually, the stands and beds are made oversize to effectively withstand the thrust forces set up during the rolling process.
With mills of the type under consideration, special importance is attached to the working roll replacement operation, and the operation involves replacement of a whole stand including the rolls to be changed with another stand, previously set up off the line and mounting new work rolls. It is for this reason that each stand is designed and built as a unit for separate handling, structurally independent of the other stands, so that it can be installed to and removed from the mill separately from the remaining stands. Each stand removably mounted in a special seat formed in the bed or load-bearing structure of the mill by securing devices, the sizing and import of which may be readily appreciated if due consideration is paid to the heavy weight of a rolling stand (on the average, in the range of about 20 to about 50 metric tons) and to the high thrust forces and stresses brought into play by the rolling process. The bed or load-bearing structure of a conventional rolling mill, as referred to herein, in addition to forming a major part thereof, involves the observance of preset interaxial distances between stands, which distances the most up-to-date rolling technologies tend to minimize, if not to eliminate (compact-design rolling mills, shortened length mandrels, and so forth).
It may be appropriate to point out that a roll change in accordance with the above-outlined prior technique involves a whole series of operations which are complicated to perform and time-consuming. In fact, the operations involved in releasing the stands from the bed of the mill, lifting the stands off and away from the mill, must be always preceded by a whole series of other operations disconnecting hydraulic and/or pneumatic line, electrical lines, etc., which operations are then to be gone through again when a new stand is connected in the roll train.
Moreover there is a disadvantage represented by the need to employ hoisting and hauling equipment of considerable size and power, which in addition to being notoriously difficult to operate, impose a large expenditure of energy, running and depreciation costs, which all add to the already substantial cost of manufacture for a stand. In this respect, it should be also considered that a rolling mill of the type in question is required to be rigged with two sets of stands for each gage, and that the consequent increase in cost and space requirements for such rigging have been long recognized in the art.
With later design mills, the rolls and their respective chocks have formed a unit adapted to be fitted into and taken off a respective stand, thereby the roll changing operation has been made much simpler and the need for replacing the stand eliminated. However, even the latter mills require periodical disassembly of the stands from their respective beds especially for maintenance and checking purposes.
Overcoming all of the disadvantages pointed out hereinabove in connection with prior rolling mills constitutes the technical problem that underlies this invention.